This occurred when attempting to play any video (I tested .mp4 .mkv .webm) on Fedora 34 Wayland session. I don't think this is a duplicate of 412422 because the backtrace is different. This is on version 0.12.0b, Frameworks 5.85.0, Qt 5.15.2. #4 0x00007fde36fa19fb in xcb_send_request_with_fds64 () from /lib64/libxcb.so.1 #5 0x00007fde36fa21dd in xcb_send_request () from /lib64/libxcb.so.1 #6 0x00007fde36fa295c in xcb_get_window_attributes () from /lib64/libxcb.so.1 #7 0x00007fde38ce23c3 in KMPlayer::VideoOutput::VideoOutput (view=<optimized out>, parent=0x561c608440b0, this=0x561c60d5a8d0) at /usr/src/debug/kmplayer-0.12.0b-4.fc34.x86_64/src/viewarea.cpp:2512 #8 KMPlayer::ViewArea::createVideoWidget (this=0x561c608440b0) at /usr/src/debug/kmplayer-0.12.0b-4.fc34.x86_64/src/viewarea.cpp:2355 #9 0x00007fde38cda8b1 in KMPlayer::MediaManager::createAVMedia (this=this@entry=0x561c607066a0, node=<optimized out>) at /usr/src/debug/kmplayer-0.12.0b-4.fc34.x86_64/src/kmplayerview.h:119 #10 0x00007fde38cde7bf in KMPlayer::MediaInfo::create (this=0x561c60c31fc0) at /usr/src/debug/kmplayer-0.12.0b-4.fc34.x86_64/src/mediaobject.cpp:686 #11 0x00007fde38cdf2d5 in KMPlayer::MediaInfo::ready (this=0x561c60c31fc0) at /usr/src/debug/kmplayer-0.12.0b-4.fc34.x86_64/src/mediaobject.cpp:715 #12 KMPlayer::MediaInfo::ready (this=0x561c60c31fc0) at /usr/src/debug/kmplayer-0.12.0b-4.fc34.x86_64/src/mediaobject.cpp:713 #13 0x00007fde38cdf660 in KMPlayer::MediaInfo::wget (this=0x561c60c31fc0, str=..., domain=...) at /usr/src/debug/kmplayer-0.12.0b-4.fc34.x86_64/src/mediaobject.cpp:487 #14 0x00007fde38ca76e0 in KMPlayer::Mrl::activate (this=0x561c60e1eb20) at /usr/src/debug/kmplayer-0.12.0b-4.fc34.x86_64/src/kmplayerplaylist.cpp:832 #15 0x00007fde38c98282 in KMPlayer::Source::play (this=0x561c60723190, mrl=0x561c60e1eb20) at /usr/src/debug/kmplayer-0.12.0b-4.fc34.x86_64/src/kmplayerpartbase.cpp:1201 #16 0x00007fde374a7809 in QObject::event (this=0x561c60723190, e=0x561c60be14d0) at kernel/qobject.cpp:1314 #17 0x00007fde37f4d423 in QApplicationPrivate::notify_helper (this=<optimized out>, receiver=0x561c60723190, e=0x561c60be14d0) at kernel/qapplication.cpp:3632 #18 0x00007fde3747d098 in QCoreApplication::notifyInternal2 (receiver=0x561c60723190, event=0x561c60be14d0) at kernel/qcoreapplication.cpp:1063 #19 0x00007fde37480606 in QCoreApplicationPrivate::sendPostedEvents (receiver=0x0, event_type=0, data=0x561c605f2000) at kernel/qcoreapplication.cpp:1817 #20 0x00007fde374cebf7 in postEventSourceDispatch (s=0x561c60641790) at kernel/qeventdispatcher_glib.cpp:277 #21 0x00007fde359374cf in g_main_context_dispatch () from /lib64/libglib-2.0.so.0 #22 0x00007fde3598b4f8 in g_main_context_iterate.constprop () from /lib64/libglib-2.0.so.0 #23 0x00007fde35934c03 in g_main_context_iteration () from /lib64/libglib-2.0.so.0 #24 0x00007fde374ce698 in QEventDispatcherGlib::processEvents (this=0x561c606987f0, flags=...) at kernel/qeventdispatcher_glib.cpp:423 #25 0x00007fde3747bab2 in QEventLoop::exec (this=this@entry=0x7ffd9d0e88b0, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:69 #26 0x00007fde37483fe4 in QCoreApplication::exec () at ../../include/QtCore/../../src/corelib/global/qflags.h:121 #27 0x00007fde378bdc60 in QGuiApplication::exec () at kernel/qguiapplication.cpp:1860 #28 0x00007fde37f4d399 in QApplication::exec () at kernel/qapplication.cpp:2824 #29 0x00007fde38f26061 in kdemain (argc=<optimized out>, argv=0x7ffd9d0e8990) at /usr/src/debug/kmplayer-0.12.0b-4.fc34.x86_64/src/main.cpp:94 #30 0x00007fde38d49b75 in __libc_start_main () from /lib64/libc.so.6 #31 0x0000561c5fcc10ae in _start ()